This project involves studies of the effects of hormones and other agents on cultured fetal rat bones and fetal rat bone cells. Emphases include: mechanism of action of parathyroid hormone, investigated by the use of ionophores; effects of vitamin D metabolites and analogs on bone in vitro and the development and use of the bone culture system as a bioassay for 1,25-(OH)2D3; effects of albumin on bone resorption in vitro, and the mechanism of action of glucocorticoids in inhibiting bone resorption. BIBLIOGRAPHIC REFERENCES: Dziak, R. and Stern, P.H. Calcium transport in isolated bone cells. III. Effects of parathyroid hormone and 3'5'-AMP. Endocrinology 97, 1281-1287, 1975. Stern, P.H., Trummel, C.L., Schnoes, H.K. and DeLuca, H.F. Bone resorbing activity of vitamin D metabolites and congeners in vitro: influence of hydroxy-substituents on the A ring. Endocrinology 97, 1552-1558, 1975.